1. Field of the Invention
This invention relates to a method for heat processing of a single crystal of silicon produced by the Czochralski process, in which method target oxygen precipitation is obtained uniformly in the direction of silicon crystal growth.
2. Description of the Related Art
It has been common knowledge that a single crystal silicon produced by the Czochralski process contains supersaturated oxygen, which is precipitated to develop oxide precipitates during heat cycles in LSI manufacture. When they are introduced into a region remote from an electronic-device-forming region, these oxide precipitates serve as the center of gettering to attract various kinds of impurities that are possibly introduced during manufacture of a LSI, thus keeping the electronic-device-forming region clean. On the other hand, when the oxide precipitates are introduced into the electronic-device-forming region, they are harmful to the electronic devices, causing deterioration of their characteristics. Consequently, for manufacturing a LSI, it is important to control the amount of precipitated oxygen in the bulk of the single crystal silicon.
The precipitation of oxygen contained in a Czochralski single crystal silicon highly depends on the initial oxygen concentration in the crystal and the heat history during the crystal growth; even in one and the same Czochralski single crystal silicon, the heat history is different between the seed crystal side and the crystal bottom side. Namely, the oxygen precipitate is large at the seed side of the single crystal silicon and small at the bottom side of the crystal silicon, thus causing a non-uniform distribution of precipitation in the crystal growth direction.